Stimulation of cyclooxygenase-2-activity by nitric oxide-derived species in rat chondrocyte: lack of contribution to loss of cartilage anabolism

Cross-talk between inducible nitric oxide synthase (NOS II) and cyclooxygen ase-2 (COX-2) was investigated in rat chondrocytes. In monolayers, interleu kin-1 beta (IL-1 beta) induced COX-2 and NOS II expression in a dose- and t ime-dependent manner, to produce high prostaglandin E-2 (PGE(2)) and nitrit e (NO2-) levels in an apparently coordinated fashion. COX-2 mRNA was induce d earlier (30 min. versus 4 hr) and less markedly (4-fold versus 12-fold at 24 hr) than NOS II, and was poorly affected by the translational inhibitor cycloheximide (CHX). IL-1 beta did not stabilize COX-2 mRNA in contrast to CHX. Indomethacin and NS-398 lacked any effect on NO2- levels whereas L-NM MA and SMT reduced PGE(2) levels at concentration inhibiting NO2- productio n from 50 to 90%, even when added at a time allowing a complete expression of both enzymes (8 hr). Basal COX activity was unaffected by NO donors. The SOD mimetic, CuDips inhibited COX-2 activity by more than 75% whereas cata lase did not. Inhibition of COX-2 by CuDips was not sensitive to catalase, consistent with a superoxide-mediated effect. In tridimensional culture, IL -1 beta inhibited radiolabelled sodium sulphate incorporation while stimula ting COX-2 and NOS II activities. Cartilage injury was corrected by L-NMMA or CuDips but not by NSAIDs, consistent with a peroxynitrite-mediated effec t. These results show that in chondrocytes: (i) COX2 and NOS II genes are i nduced sequentially and distinctly by IL-1 beta; (ii) COX-1 and COX-2 activ ity are affected differently by NO-derived species; (iii) peroxynitrite acc ounts likely for stimulation of COX-2 activity and inhibition of proteoglyc an synthesis induced by IL-1 beta. (C) 2001 Elsevier Science Inc. All right s reserved.